In the disclosure of the present invention reference is mostly made to the treatment of diabetes by injection or infusion of insulin, however, this is only a preferred use of the present invention.
In order to permit a patient to administer a proper dose, various mechanical injection devices have been proposed such as the devices shown in WO 01/95959 and WO 2008/116766. Some devices incorporates additional electric circuitry for measuring and displaying the size of a dose which is being set during a dose setting procedure or which is being administered during an injection procedure. Examples of such devices are shown in WO 02/092153 and in WO 02/064196.
In terms of safety, it is generally preferred that both movements during dose setting and during dose injection are being monitored. However, it remains a challenge to design a system which provides adequate reliability and robustness and which at the same time enables the device to be manufactured in an inexpensive way.
WO 2008/037801 includes disclosure of an injection device wherein separate sensor systems are respectively associated with a dose setting mechanism and an injection mechanism. Such sensor configuration may offer additional reliability having regard to the monitoring of the components which moves during dose setting and during injection. However, the described choice of sensor circuitry may prove difficult to calibrate and hence may prove expensive to manufacture.
Another problem with some existing injection devices is that potential liquid ingress into the interior of the injection device, such as fluid drug leaking from a held cartridge, may render the operation of the device inoperable or faulty.
The reference US 2003/0009131 A1 deals with measures for detecting fluid that leaks outside normal fluid paths in a fluid delivery system. The references includes disclosure of fluid detectors arranged on or near the reservoir which containing the fluid to be delivered into an individual's body. A related system is described in U.S. Pat. No. 4,787,645.
Having regard to the above-identified prior art devices, It is an object of the invention to provide an electronically assisted injection device in which the monitoring of movements of the mechanical components during operation of the device is accurately and safely performed.
It is a further object of the invention to provide an electronically assisted injection device that may be manufactured in an inexpensive way.
It is a further object of the invention to provide an electronically assisted injection device in which it is possible to control movements of the piston rod in a more accurate manner than in similar prior art devices and to utilize this for improving the reliability of the electronic monitoring of positional information relating to particular components of the injection device.
It is a further object of the invention to provide an electronically assisted injection device which provides improvements in the detection of potential fluid ingress into interior parts of the injection device.